Alkyne-Isocyanide Coupling in [Fe2(CNMe)(CO)3(Cp)2]: A NewRoute to Diiron µ-Vinyliminium Complexes†

Vincenzo G. Albano,‡ Luigi Busetto,*,§ Fabio Marchetti,| Magda Monari,‡Stefano Zacchini,§ and Valerio Zanotti§

Dipartimento di Chimica Fisica e Inorganica, UniVersita di Bologna, Viale Risorgimento 4,40136 Bologna, Italy, Dipartimento di Chimica “G. Ciamician”, UniVersita di Bologna, Via Selmi 2,

40126 Bologna, Italy, and Dipartimento di Chimica e Chimica Industriale, UniVersita di Pisa,Via Risorgimento 35, I-56126 Pisa, Italy

ReceiVed February 1, 2007

Alkynes (RCtCR′) insert into the metal-isocyanide bond of [Fe2(CNMe)(CO)3(Cp)2] (1), under UVirradiation, affording the complexes [Fe2{µ-η1:η3-C(R)C(R′)CdN(Me)}(µ-CO)(CO)(Cp)2] (R ) R′) Ph,2a; R ) R′ ) Me, 2b; R ) R′ ) Et, 2c; R ) Ph, R′ ) H, 2d; R ) Tol, R′ ) H, 2e; R ) SiMe3, R′ )H, 2f; R ) Me, R′ ) H, 2g; R ) CH2OH, R′ ) H, 2h; Tol ) 4-MeC6H4), with displacement of one COligand. Compounds2b,c exist as a mixture of cis and trans isomers (with reference to the mutual Cpposition), whereas2a,d-h exclusively have the cis geometry. The insertion of terminal alkynes isregioselective, since C-C bond formation occurs selectively between the isocyanide and the nonsubstitutedcarbon of HCtCR. Compound1 reacts with 2 equiv of HCtCCO2Me under UV irradiation, affording[Fe2{µ-η2:η4-C(OH)C(CO2Me)C(H)CN(Me)(CHdCHCO2Me}(CO)(Cp)2] (4). Complexes2a,c undergoelectrophilic addition at the N atom by treatment with HSO3CF3, allyl iodide (ICH2CHdCH2), and methylchloroformate (ClCOOMe), affording the corresponding vinyliminium cations [Fe2{µ-η1:η3-C(R)dC(R)CdN(Me)(E)}(µ-CO)(CO)(Cp)2]+ (R ) Ph, E) H, 5a; R ) Et, E ) H, 5b; R ) Ph, E) CH2CHdCH2,6; R ) Ph, E ) CO2Me, 7). The reactions of6 with NaBH4 and NBu4CN afford [Fe2{µ-η1:η3-C(Ph)C(Ph)dC(H)N(Me)(CH2CHdCH2)}(µ-CO)(CO)(Cp)2] (8) and [Fe2{µ-η1:η3-C(Ph)C(Ph)C(CN)N(Me)-(CH2CHdCH2)}(µ-CO)(CO)(Cp)2] (9), respectively. The molecular structures ofcis-2c, [Fe2{µ-η1:η3-C(Et)dC(Et)C)N(Me)(Xyl)}(µ-CO)(CO)(Cp)2][SO3CF3] (3), 4, and5a have been established by X-raydiffraction studies.

Introduction

The transition-metal-promoted conversion of C1 ligands intoorganic compounds remains a major goal in organometallicchemistry. In this context, the insertion of alkynes into themetal-carbon bond of bridging CO,1 µ-alkylidenes,2 andµ-alkylidynes3 provides an efficient route to the C-C bondformation in dinuclear complexes. These reactions, whichgenerally result in the formation of C3-bridged species, haveattracted great attention because of the implications with thecarbon-carbon chain growth in the Fischer-Tropsch (FT)process.4

Our work in this area has shown that the coupling of C1

(aminocarbyne) and C2 (alkyne) units affords C3 bridgingvinyliminium species (Scheme 1).5,6

These latter species have been further modified and havegrown in complexity by introduction of new functionalities,

under regio- and stereoselective conditions. Indeed, we havereported that the bridging vinyliminium ligands undergo avariety of transformations upon addition of hydride,7 cyanide,8

acetylides,9 and organolithium reagents.10 Further modifications

* To whom correspondence should be addressed. E-mail: luigi.busetto@unibo.it.

† Dedicated to Professor Robert J. Angelici on the occasion of his 70thbirthday.

‡ Dipartimento di Chimica “G. Ciamician”, Universita` di Bologna.§ Dipartimento di Chimica Fisica e Inorganica, Universita` di Bologna.| Universitadi Pisa.(1) (a) Dyke, A. F.; Knox, S. A. R.; Naish, P. J.; Taylor, G. E.J. Chem.

Soc., Chem. Commun. 1980, 409. (b) Davies, D. L.; Dyke, A. F.; Knox, S.A. R.; Morris, M. J.J. Organomet. Chem.1981, 215, C30-C32. (c) Dyke,A. F.; Knox, S. A. R.; Naish, P. J.; Taylor, G. E.J. Chem. Soc., DaltonTrans. 1982, 1297. (d) Gracey, B. P.; Knox, S. A. R.; Macpherson, K. A.;Orpen, A. G.; Stobart, S. R.J. Chem. Soc., Dalton Trans.1985, 1935. (e)Fontaine, X. L. R.; Jacobsen, G. B.; Shaw, B. L.; Thornton-Pett, M. J. Chem.Soc., Dalton Trans.1988, 741.

(2) (a) Dyke, A. F.; Knox, S. A. R.; Naish, P. J.; Taylor, G. E.J. Chem.Soc., Chem. Commun. 1980, 803. (b) Sumner, C. E.; Collier, J. A.; Pettit,R. Organometallics1982, 1, 1350. (c) Adams, P. Q.; Davies, D. L.; Dyke,A. F.; Knox, S. A. R.; Mead, K. A.; Woodward, P.J. Chem. Soc., Chem.Commun. 1983, 222. (d) Levisalles, J.; Rose-Munch, F.; Rudler, H.; Daran,J. C.; Jeannin, Y.J. Organomet. Chem.1985, 279, 413. (e) Akita, M.; Hua,R.; Nakanishi, S.; Tanaka, M.; Moro-oka, Y.Organometallics1987, 16,5572. (f) Navarre, D.; Parlier, A.; Rudler, H.; Daran, J. C.J. Organomet.Chem.1987, 322, 103. (g) Colburn, R. E.; Davies, D. L.; Dyke, A. F.;Knox, S. A. R.; Mead, K. A.; Orpen, A. G.J. Chem. Soc., Dalton Trans.1989, 1799. (h) Knox, S. A. R.J. Organomet. Chem.1990, 400, 255. (i)Kaneko, Y.; Suzuki, T.; Isobe, K.; Maitlis, P. M.J. Organomet. Chem.1998, 554. (j) Royo, E.; Royo, P.; Cuenca, T.; Galakhov, M.Organome-tallics 2000, 19, 5559. (k) Rowsell, B. D.; McDonald, R.; Ferguson, M. J.;Cowie, M.Organometallics2003, 22, 2944. (l) Wigginton, J. R.; Chokshi,A.; Graham, T. W.; McDonald, R.; Ferguson, M. J.; Cowie, M.Organo-metallics2005, 24, 6398.

Scheme 1

3448 Organometallics2007,26, 3448-3455

10.1021/om070097z CCC: $37.00 © 2007 American Chemical SocietyPublication on Web 06/06/2007

of the bridging vinyliminium ligand have also been found, owingto the acidic character of the Câ-H.11

Herein we report on the extension of these studies to thealkyne-isocyanide coupling in the diiron complex [Fe2(CNMe)-(CO)3(Cp)2] (1). To the best of our knowledge, the reactivityof 1 toward alkynes is still unexplored, in spite of the fact thatthe chemistry of isocyanide complexes has been extensivelyinvestigated in the past.12

Results and Discussion

Alkyne Insertion into the Metal -Isocyanide Bond.Thecomplex [Fe2(CNMe)(CO)3(Cp)2] (1) consists of an isomericmixture of terminal and bridging isocyanide, with a largeprevalence of the second form.13 The reactions of1 with mono-and disubstituted alkynes RCtCR′, under UV irradiation inEt2O solution, result in the formation of [Fe2{µ-η1:η3-C(R)C(R′)CdN(Me)}(µ-CO)(CO)(Cp)2] (2a-h) in about 60%yield (Scheme 2).

The synthesis of2a-h is the result of alkyne insertion intothe metal-isocyanide bond of1, promoted by photochemicalloss of a CO ligand. All the compounds have been purified bycolumn chromatography on alumina and characterized by IRand NMR spectroscopy and elemental analysis. The structureof 2c has been determined by X-ray diffraction. The ORTEPmolecular diagram is shown in Figure 1, and relevant bondlengths and angles are reported in Table 1. This is the firststructural study for this family of compounds in which themultibridging ligand bears an imine fragment. The electronicstructure of the N-CR-Câ-Cγ unit can be schematized in threedifferent ways: (A) allylimine, (B) enimine (azabutadienyl), and(C) ketenimine. As a consequence, the ligand-metal bondinginteractions can be described differently, as shown in Chart 1.An analysis of the bond parameters is necessary in order to findout the best representation of the electronic structure of this

(3) (a) Jeffery, J. C.; Mead, K. A.; Razay, H.; Stone, F. G. A.; Went, M.J.; Woodward, P.J. Chem. Soc., Dalton Trans. 1984, 1383. (b) Chisholm,M. H.; Heppert, J. A.; Huffman, J. C.J. Am. Chem. Soc.1984, 106, 1151.(c) Seyferth, D.; Ruschke, D. P.; Davis, W. M.Organometallics1994, 13,4695. (d) Casey, C. P.; Woo, L. K.; Fagan, P. J.;Palermo, R. E.; Adams, B.R. Organometallics1987, 6, 447.

(4) (a) Maitlis, P. M.J. Organomet. Chem.2004, 689, 4366. (b) Turner,M. L.; Marsih, N.; Mann, B. E.; Quyoum, R.; Long, H. C.; Maitlis, P. M.J. Am. Chem. Soc.2002, 124, 10456. (c) Overett, M. J.; Hill, R. O.; Moss,J. R. Coord. Chem. ReV. 2000, 206-207, 581-605. (d) Roberts, M. W.Chem. Soc. ReV. 1977, 6, 373-391. (e) Cowie, M.Can. J. Chem.2005,83, 1043-1055.;

(5) (a) Albano, V. G.; Busetto, L.; Marchetti, F.; Monari, M.; Zacchini,S.; Zanotti, V.Organometallics2003, 22, 1326. (b) Albano, V. G.; Busetto,L.; Marchetti, F.; Monari, M.; Zacchini, S.; Zanotti, V.J. Organomet. Chem.2004, 689, 528.

(6) Busetto, L.; Marchetti, F.; Zacchini, S.; Zanotti, V.J. Organomet.Chem. 2006, 691, 2424.

(7) (a) Albano, V. G.; Busetto, L.; Marchetti, F.; Monari, M.; Zacchini,S.; Zanotti, V.Organometallics2004, 23,3348. (b) Albano, V. G.; Busetto,L.; Marchetti, F.; Monari, M.; Zacchini, S.; Zanotti, V.J. Organomet. Chem.2005, 690, 837.

(8) Albano, V. G.; Busetto, L.; Marchetti, F.; Monari, M.; Zacchini, S.;Zanotti, V. J. Organomet. Chem. 2006, 691, 4234.

(9) Busetto, L.; Marchetti, F.; Zacchini, S.; Zanotti, V.Eur. J. Inorg.Chem.2006, 285.

(10) Albano, V. G.; Busetto, L.; Marchetti, F.; Monari, M.; Zacchini,S.; Zanotti, V.J. Organomet. Chem. 2005, 690, 4666.

(11) Busetto, L.; Marchetti, F.; Zacchini, S.; Zanotti, V.Organometallics2005, 24, 2297.

(12) (a) Adams, R. D.; Cotton, F. A.Synth. React. Inorg. Met.-Org. Chem.1974, 4, 477. (b) Adams, R. D.; Cotton, F. A.Inorg. Chem. 1974, 13, 249.(c) Bellerby, J.; Boylan, M. J.; Ennis, M.; Manning, A. R.J. Chem. Soc.,Dalton Trans,1978, 1185. (d) McNally, G.; Murray, P. T.; Manning, A.R. J. Organomet. Chem.1983, 243, C87. (e) Fehlhammer, W. P.; Mayr,A.; Kehr, W.; J. Organomet. Chem.1980, 197, 327.

(13) Adams, R. D.; Cotton, F. A.; Troup, J. M.Inorg. Chem.1974, 13,257.

Scheme 2

Figure 1. ORTEP drawing ofcis-[Fe2{µ-η1:η3-C(Et)C(Et)CdN(Me)}(µ-CO)(CO)(Cp)2] (2c). Hydrogen atoms are omitted forclarity; thermal ellipsoids are given at the 30% probability level.

Table 1. Selected Bond Lengths (Å) and Angles (deg) for 2c,3, and 5a

2c 3 5aa

Fe(1)-C(1) 1.866(3) 1.949(4) 1.962(6) [1.981(6)]Fe(2)-C(1) 1.949(3) 1.896(4) 1.867(6) [1.887(6)]Fe(1)-C(3) 2.029(2) 2.030(4) 2.059(5) [2.047(5)]Fe(2)-C(3) 1.967(2) 1.976(4) 1.960(5) [1.973(5)]Fe(1)-C(4) 2.056(3) 2.073(4) 2.105(4) [2.103(5)]Fe(1)-C(5) 1.952(3) 1.853(4) 1.832(5) [1.841(5)]C(1)-O(1) 1.186(3) 1.163(5) 1.177(6) [1.166(6)]Fe(1)-Fe(2) 2.5249(7) 2.5532(8) 2.560(1) [2.554(1)]C(2)-O(2) 1.135(4) 1.130(6) 1.132(7) [1.138(7)]C(3)-C(4) 1.427(4) 1.410(6) 1.430(7) [1.424(7)]C(4)-C(5) 1.431(4) 1.444(5) 1.421(7) [1.428(7)]C(5)-N(1) 1.237(4) 1.292(5) 1.289(6) [1.27886)]C(10)-N(1) 1.470(4)C(6)-N(1) 1.484(5) 1.468(7) [1.466(7)]C(9)-N(1) 1.455(5)Fe(1)-C(Cp) (av) 2.094 2.099 2.096 [2.103]Fe(2)-C(Cp) (av)b 2.115 2.116 2.119 [2.136]

C(3)-C(4)-C(5) 117.1(2) 114.9(3) 114.3(4) [114.3(4)]N(1)-C(5)-C(4) 137.1(2) 132.7(3) 131.7(5) [133.4(5)]C(5)-N(1)-C(10) 120.0(3)C(5)-N(1)-C(9) 121.1(3)C(5)-N(1)-C(6) 122.0(4) 124.5(5) [124.8(5)]C(6)-N(1)-C(9) 116.8(3)C(5)-N(1)-H(1) 116(4) [118(4)]

a Data for the second conformer of5aare given in brackets.b Main imageof the Cp ligand.

Chart 1

Diiron µ-Vinyliminium Complexes Organometallics, Vol. 26, No. 14, 20073449

unconventional NC3Fe2 grouping. The C(5)-N(imine) interac-tion (1.237(4) Å) indicates a localized double bond. (Comparethis value with the genuine single bond N-C(10)(methyl))1.470(4) Å.) The torsion angle in the chain Cγ-Câ-CR-N(C(3)-C(4)-C(5)-N ) 39.0(3)°) is high for an efficientπ-bond delocalization, as required by structuresA and C.Therefore, a good approximation of the electronic structure ofthe NC3 fragment is as azabutadienyl (B) and its interactionwith the Fe2 core isη1 to Fe(2) andη1:η2 to Fe(1). The degreeof nonequivalence of the iron atoms in this asymmetric moleculeis assessed by the bonding asymmetry of the bridging carbonyl(Fe(1)-C(1) ) 1.866(3) Å, Fe(2)-C(1) ) 1.949(3) Å). Theshorter distance from Fe(1) indicates greater donation to thisatom to which CR (C(5)) acts essentially as a one-electron donor,its pz orbital being primarily engaged in the localizedπ bondto N. The quite long Fe(1)-C(5) distance (1.952(3) Å) is inaccord with this interpretation.

The bridging ligand in the neutral complex2c is strictlyrelated to the analogous grouping present in the cationic [Fe2-{µ-η1:η3-C(Et)dC(Et)CdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][SO3-CF3] (3).5b Complex3 is formally derived from2c by additionof a Xyl+ fragment at the nitrogen atom. In order to ascertainthe structural effects of a second substituent of the nitrogen atom,we have now determined the X-ray structure of3. The moleculardiagram is shown in Figure 2, and relevant bond lengths andangles are given in Table 2. Expectedly, we find that the bondparameters in3 are comparable, within experimental error, tothose already reported for [Fe2{µ-η1:η3-C(Me)dC(Me)CdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][SO3CF3].5b A comparison with

2c reveals the effects of changing the nature of the nitrogenfrom imine to iminium. The bonding interactions of Cγ (C(3))and Câ (C(4)) are substantially unaffected, while CR (C(5))exhibits significant variations. The CR-N bond is lengthenedwith respect to2c (1.292(5) vs 1.237(4) Å). This lengtheningis accompanied by a shortening of the CR-Fe bond (C(5)-Fe(1): 1.853(4) vs 1.952(3) Å). These figures indicate that thepz orbital on CR is less involved inπ bonding to N and moreinvolved in bonding to Fe(1). The result is a higher electrondonation to the metal with respect to2c. This rationalization isconfirmed by the inversion of the asymmetry of the bridgingcarbonyl, which is now farther from Fe(1) (Fe(1)-C(1) )1.949(4) Å and Fe(2)-C(1) ) 1.896(4) Å vs 1.866(3) and1.949(3) Å in2c), while the other bond interactions of Fe(1)are slightly (but not significantly) lengthened. The electronicstructure of the N-CR-Câ-Cγ grouping is not significantlychanged with respect to the neutral species2c, and the systemcan still be described as azabutadienyl with a torsion angle alongthe chain N-C(5)-C(4)-C(3) (34.7(4)° in 3 vs 39.0(3)° in 2c).

The IR spectra (in CH2Cl2 solution) of2a-h exhibit a weakabsorption in the range 1714-1740 cm-1, attributable to theimine CR-N bond and the usualν(CO) band pattern (e.g., for2a at 1972 and 1788 cm-1).

Several isomeric forms are, in theory, possible for2a-h dueto the mutual Cp position (cis and trans isomers) or to the twopossible orientations of the N-Me group in the imine moiety(E and Z isomers). Nonetheless, NOE studies, carried out oncompounds2a-c, indicate that these species adopt aZ config-uration in solution, in agreement with the geometry found inthe solid state. Moreover,2aexists only in the cis form, whereasboth cis and trans isomers are present in the case of2b,c.Mixtures of 2b,c as the cis and trans isomers have beencompletely converted into the more stablecis-2b and cis-2c,upon heating at reflux temperature in toluene for 2 h.

For complexes2d-h, obtained by insertion of unsymmetricalkynes, a third type of isomerism is possible, due to theinsertion mode of the primary alkynes. Interestingly, the1HNMR spectra of2d-h exhibit a single set of resonances,indicating that the insertion reaction is regioselective. Inparticular, the1H NMR spectra show that the CH portion ofthe inserted HCCR generates a resonance at aboutδH 2.85-3.19 ppm, as expected for Câ-H. In contrast, the alternativeisomer (Cγ-H) would resonate in the higher frequency rangeof methylidene protons. NOE experiments confirm that thebridging chain sequence is N-CR-Câ(H)-Cγ(R) and givefurther information on the geometry of the complexes insolution: the Cp ligands are mutually cis and the imine N-Megroup is in theZ configuration, as found in the solid state for2c.

Major features of the13C NMR spectra of2a-h include theCR carbon resonance at about 195 ppm and the Cγ resonancein the 180-200 ppm range, which are consistent with theiriminoacyl and alkylidene nature. Conversely, the Câ resonanceis found at ca. δ 50 ppm.

The reaction described in Scheme 2 deserves further com-ment. Metal-assisted coupling reactions between alkynes andisocyanides are known for both mononuclear14 and dinuclearcomplexes of Mn,15 Os,16 and Rh.17 Among these examples onlythe dirhodium complex [Rh2Cp2(CO){µ-C(NR)C(CF3)C(CF3)]

(14) (a) Adams, C. J.; Anderson, K. M.; Bartlett, I. M.; Connelly, N.G.; Orpen, A. G.; Paget, T. J.Organometallics2002, 21, 3454. (b) Barnea,E.; Andrea, T.; Kapon, M.; Berthet, J. C.; Ephritikhine, M.; Eisen, M. S.J.Am. Chem. Soc.2004, 126, 10860. (c) Werner, H.; Heinemann, A.;Windmueller, B.; Steinert, P.Chem. Ber.1996, 129, 903.

(15) Adams, R. D.; Mingsheng, H.;Organometallics,1995, 14, 506.

Figure 2. ORTEP drawing of the cation of (cis,Z)-[Fe2{µ-η1:η3-C(Et)dC(Et)CdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][CF3SO3] (3). Hy-drogen atoms are omitted for clarity; thermal ellipsoids are givenat the 30% probability level.

Table 2. Selected Bond Lengths (Å) and Angles (deg) for[Fe(Cp){η5-Fe(Cp)(CO){µ-η2-C{N(Me)(CHdCHCO2Me)}-

CHC(CO2Me)C(OH)}] (4)

Fe(1)-Fe(2) 2.5561(13) C(5)-C(1) 1.415(9)Fe(1)-C(1) 2.017(6) C(5)-C(6) 1.469(9)Fe(2)-C(1) 1.907(7) C(6)-O(3) 1.311(9)Fe(2)-C(3) 1.988(6) O(3)-C(7) 1.441(8))Fe(1)-C(3) 1.986(6) N(1)-C(9) 1.365(9)Fe(1)-C(4) 2.014(6) C(9)-C(10) 1.35(1)Fe(1)-C(5) 2.022(7) C(11)-O(6) 1.35(1)Fe(2)-C(2) 1.737(7) O(6)-C(12) 1.47(1)C(1)-O(1) 1.379(8) C(11)-O(5) 1.18(1)C(2)-O(2) 1.149(9) N(1)-C(8) 1.441(8)C(3)-N(1) 1.412(8) Fe(1)-C(Cp) (av) 2.063C(3)-C(4) 1.459(9) Fe(2)-C(Cp) (av) 2.111C(4)-C(5) 1.430(9)

Fe(1)-C(1)-O(1) 128.6(5) C(3)-N(1)-C(9) 118.8(5)Fe(2)-C(1)-O(1) 122.8(4) C(4)-C(5)-C(6) 121.8(6)C(4)-C(3)-N(1) 117.9(5) C(8)-N(1)-C(9) 119.3(6)C(1)-Fe(2)-C(3) 82.0(3) C(4)-C(5)-C(1) 113.5(6)Fe(2)-C(3)-C(4) 111.8(4) C(5)-C(1)-Fe(2) 115.8(5)C(3)-C(4)-C(5) 112.6(5)

3450 Organometallics, Vol. 26, No. 14, 2007 Albano et al.

has a bridging enimine ligand with a structure and coordinationmode similar to that found in2a-h.17 Indeed, alkyne-isocyanide couplings present a variety of outcomes, mostly asa consequence of multiple insertions, rearrangements, or inclu-sion of other molecular fragments. Moreover, theµ-η1:η3

coordination described above is not the only way for an enimine(azabutadienyl) fragment to bridge two metal centers.18 Ac-cording to the variety of possible combinations between alkynesand isocyanides, not all the reactions that we have investigatedproceed as described in Scheme 2. This is the case of thereaction of1 with methyl propiolate, which under the samereaction conditions as for2a-h affords complex4, with notrace of the expected analogue of2a-h (Scheme 3). Even whenthe reaction was performed with 1 equiv of HCtCCO2Me,instead of a large excess, compound4 was the only identifiedproduct, although formed in lower yield. Complex4 has beenisolated by chromatography and characterized by spectroscopyand X-ray diffraction. The ORTEP molecular diagram is shownin Figure 3, whereas relevant bond lengths and angles arereported in Table 2.

The reaction sequence leading to the formation of4 is farfrom being understood and involves displacement of one COligand from 1, combination of two HCtCCO2Me moleculeswith the isocyanide and the bridging CO ligand, and the additionof two hydrogen atoms. One propiolate molecule is terminallyadded to the nitrogen atom, giving the dangling chain that doesnot interact with the metal core. The other propiolate moleculeundergoes further rearrangements which involve addition to thecarbon atoms of the bridging ligands: i.e., the isocyanide (C(3))and bridging carbonyl (C(1)). The resulting fragment is engaged

in η4 coordination to one metal atom (Fe(1)). Compound4 canbe described as being composed of a [Fe2(Cp)2(CO)] moietycoordinated by a bridgingµ-η2:η4-{C(OH)dC(CO2Me)C(H)dCN(Me)(CHdCHCO2Me)} ligand (Scheme 3). A more appeal-ing rationalization of the molecular architecture can be inferredfrom the following geometrical features: the atoms C(3)-C(4)-C(5)-C(1)-Fe(2) form a five-membered ring described asmetallacyclopentadienyl (deviations from the average plane inthe range-0.06 to+0.12 Å, C-C distances in the range 1.42-1.46(1) Å, C(1,3)-Fe(2) distances 1.91 and 1.99(1) Å). Themetalla ring is almost parallel to the Cp ring (C(13)-C(17))bound to Fe(1) (dihedral angle 10.3(4)°). In conclusion, themolecule can be viewed as a ferrocene analogue, in which onering incorporates one metal atom (Fe(2)) and has differentsubstituents containing heteroatoms (Chart 2).

The IR spectrum of4 (in CH2Cl2 solution) shows one terminalν(CO) absorption, at 1965 cm-1, together with two absorptionsattributable to the carboxylate groups (at 1686 and 1672 cm-1)and a band due toν(CdC) at 1601 cm-1. The1H NMR spectrumexhibits two separate resonances for the inequivalent Cp rings(atδ 4.94 and 4.31 ppm). Four singlets (atδH 10.00, 5.24, 3.74,and 3.31 ppm) are attributable to the OH, CâH, carboxylatemethyl, and N-bound methyl, respectively. Moreover, theprotons of the enamine moiety resonate as doublets at 8.35 and4.90 ppm. Finally, the carbon atoms of the metallacyclopenta-dienyl ring resonate, in the13C NMR spectrum, at 179.0 (CR),79.3 (Câ), 67.2 (Cγ), and 216.6 (COH) ppm, respectively.

Formation of Vinyliminium Complexes. The reactivity ofthe bridging enimine (azabutadienyl) ligand in2a-h was theninvestigated. Conversion of2a-h into the correspondingvinyliminium species [Fe2{µ-η1:η3-C(R)dC(R′)CdN(Me2)}(µ-CO)(CO)(Cp)2][CF3SO3] appears to be possible simply viaN-methylation. For instance,2ereacts with 1 equiv of CF3SO3-CH3, in dichloromethane solution, to give the known vinyl-iminium complex [Fe2{µ-η1:η3-C(Tol)dC(H)CdN(Me)2}(µ-CO)(CO)(Cp)2][CF3SO3]5a in almost quantitative yield. Likewise,the reactions of2a and (cis + trans)-2c with HBF4 result inthe formation of the new vinyliminium species [Fe2{µ-η1:η3-C(R)dC(R)CdN(Me)(H)}(µ-CO)(CO)(Cp)2][BF4] (R ) Ph,5a;R ) Et, 5b) (Scheme 4). The reaction is completely reversible,and the parent complexes are recovered after treatment of5a,bwith Et3N.

It should be noted that vinyliminium complexes of type5are not otherwise obtainable, because the usual approach,consisting of alkyne insertion into the aminocarbyne complex,

(16) Huang, J.-Y.; Lin, J.-J.; Chi, K.-M.; Lu, K.-L.J. Chem. Soc., DaltonTrans. 1997, 15.

(17) Dickson, R. S.; Fallon, G. D.; Nesbit, R. J.; Pateras, H.Organo-metallics1987, 6, 2517.

(18) Lemke, F. R.; Szalda, D. J.; Bullock, R. M.Organometallics1992,11, 876.

Figure 3. ORTEP drawing of [Fe2{µ-η2:η4-C(OH)C(CO2Me)C-(H)CN(Me)(CHdCHCO2Me}(CO)(Cp)2] (4). Only the hydrogenatom bound to O(1) is shown. Thermal ellipsoids are given at the30% probability level.

Scheme 3

Chart 2

Scheme 4

Diiron µ-Vinyliminium Complexes Organometallics, Vol. 26, No. 14, 20073451

is unsuccessful in the case of [Fe2{µ-CN(Me)(H)}(µ-CO)(CO)2-(Cp)2]+.19 Indeed, this latter species, upon treatment with alkynesin the presence of Me3NO, undergoes deprotonation rather thanalkyne insertion.

Complex 5a has been structurally characterized by X-raycrystallography (Figure 4, and Table 1). In the crystal twoconformers of the cation of [Fe2{µ-η1:η3-C(Ph)dC(Ph)CdN(Me)(H)}(µ-CO)(CO)(Cp)2][BF4] (5a) are present. Since thedifference between the two conformers resides in the mutualorientation of the phenyl rings, only the stereogeometry of oneis represented in Figure 4, whereas relevant bond lengths andangles for both are reported in Table 1. The molecular structureof 5a closely resembles those of the related vinyliminiumcomplexes [M2{µ-η1:η3-C(R′)dC(R′′)CdN(Me)(R)}(µ-CO)-(CO)(Cp)2][SO3CF3],5 as can be inferred by a comparison ofthe corresponding bond distances and angles. The iminium grouppresents aZ conformation, with the N-Me group pointing inthe opposite direction with respect to the Câ-Ph group.

The IR spectrum of5a (in CH2Cl2 solution) exhibits twobands due to the terminal and bridging carbonyls, at 2004 and1804 cm-1, respectively. Moreover, a sharp band, due toν(NH),is observed at 3246 cm-1 (in KBr pellets). The1H NMRspectrum of5a reveals the presence of two isomers in solution,in an 8:5 ratio. These have been identified as (cis,E)-5a and(cis,Z)-5a (Chart 3), on the basis of NOE investigations. TheNH proton gives rise to a broad resonance at low field (10.37ppm). Relevant13C NMR features include the resonances ofCR, Câ, and Cγ (at δ 226.5, 71.8, and 200.8 ppm, respectively,for (cis,E)-5a), in the range typical for vinyliminium ligands.5

Conversely, the IR spectrum of5b (in CH2Cl2 solution) suggeststhe presence of a mixture of cis and trans isomers: the carbonylabsorptions related to the cis isomer are found at 2000 and 1807cm-1, and those of the trans isomer are at 1978 and 1789 cm-1.

The presence of an isomeric mixture is well evidenced inthe 1H NMR spectrum of5b, which exhibits two sets ofresonances in a 6:1 ratio. NOE studies indicate that the majorisomer is (trans,Z)-5b, whereas the minor species is (cis,Z)-5b(Chart 3). The presence of cis and trans isomers is consistentwith the fact that the parent compound2calso contains a mixtureof cis and trans isomers. However, also the reaction of purecis-2c with HBF4 affords a mixture ofcis-5b and trans-5b,suggesting that the observed isomeric mixture corresponds toan equilibrium composition. This hypothesis is also strengthened

by the observation that the isomer ratio does not change uponheating at reflux temperature, in THF, for 120 min. Thesefindings appear in contrast with the behavior of disubstitutedvinyliminium complexes of the type [Fe2{µ-η1:η3-C(R)dC(R)CdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][CF3SO3] (R ) Me, Et),5b inwhich the trans isomer is easily converted into the cis speciesby heating at reflux temperature in THF.

The nucleophilic character of the imine nitrogen in2 can befurther exploited to prepare new N-functionalized vinyliminiumcomplexes. Thus,2a reacts with allyl iodide (ICH2CHdCH2)and methyl chloroformate (ClCOOMe), affording the species[Fe2{µ-η1:η3-C(Ph)dC(Ph)CdN(Me)(CH2CHdCH2)}(µ-CO)-(CO)(Cp)2][I] ( 6) and [Fe2{µ-η1:η3-C(Ph)dC(Ph)CdN(Me)-(COOMe)}(µ-CO)(CO)(Cp)2][Cl] ( 7), respectively (Scheme 5).Compounds6 and7 have been fully characterized by IR andNMR spectroscopy, elemental analysis, and mass spectrometry(see the Experimental Section). Their properties resemble thoseof related vinyliminium complexes.5 Complex 6 exists insolution as mixture of cis,E and cis,Z isomers, in comparableamounts, as indicated by NOE investigations. In contrast, the1H NMR spectrum of complex7 shows a single set ofresonances, but it has not been possible to establish theconfiguration adopted by the nitrogen substituents.

Complexes6 and7 are of interest because the vinyliminiumcomplexes so far reported have been limited to species contain-ing the CRN(Me)(R) fragment, in which R) Me, CH2Ph, Xyl.In fact the ligand is generated from the bridging aminocarbyneCN(Me)R, which, in turn, is conveniently obtained fromavailable isocyanides (CNR) and strong alkylating agents

(19) Willis, S.; Manning, A. R.; Stephens, F. S.J. Chem. Soc., DaltonTrans. 1979, 23.

Figure 4. ORTEP drawing of the cation of [Fe2{µ-η1:η3-C(Ph)dC(Ph)CdN(Me)(H)}(µ-CO)(CO)(Cp)2][BF4] (5a). Only the hydro-gen atom bound to N(1) is shown. Thermal ellipsoids are given atthe 30% probability level.

Chart 3

Scheme 5

3452 Organometallics, Vol. 26, No. 14, 2007 Albano et al.

(MeSO3CF3). Thus, the synthesis of6 and7 demonstrates thatnitrogen functionalization can be extended to a range of differentsubstituents, overcoming the aforementioned limits.

It has been previously shown that the substituents on theiminium nitrogen influence the reactivity of the ligand. Indeed,the Xyl group exerts a “steric protection” on the iminium carbon(CR), the most reactive site of the ligand, and hinders the additionof hydride or cyanide at that position.7,8 The syntheses of6 and7 provide the opportunity to extend the investigations andobserve possible effects due to the allyl or carboxylate groups.Therefore, the reactions of6 and7 with NaBH4 and [(NBu4)-(CN)] have been studied. Unexpectedly, the reactions of7 withH- or CN- simply reverse the alkylation step and result in theformation of the parent complex2a. The reaction of6 withNaBH4 affords the enamino-alkylidene compound [Fe2{µ-η1:η3-C(Ph)C(Ph)dC(H)N(Me)(CH2CHdCH2)}(µ-CO)(CO)-(Cp)2] (8), while with (NBut

4)(CN) the result is the formationof the cyano-functionalized allylidene species [Fe2{µ-η1:η3-C(Ph)C(Ph)C(CN)N(Me)(CH2CHdCH2)}(µ-CO)(CO)(Cp)2] (9)(Scheme 6). Compounds8 and9 have been fully characterizedby spectroscopy (see the Experimental Section), and theirproperties are consistent with those of strictly related com-pounds.7,8

The results shown in Scheme 6 are consistent with thenucleophilic attack at CR exhibited by the vinyliminiumcomplexes [Fe2{µ-η1:η3-C(R′)dC(R′′)CdN(Me)(R)}(µ-CO)-(CO)(Cp)2][SO3CF3] (R ) Me, CH2Ph; R′ ) Me, Tol, SiMe3,COOMe, R′′ ) H; R′ ) R′′ ) Me, Et, COOMe) in theirreactions with NaBH47 and [(NBu4)(CN)].8

Conclusions

Photochemical reactions of the diiron isocyanide complex[Fe2(CNMe)(CO)3(Cp)2] with alkynes yield novel bridgingenimine complexes by alkyne insertion into the metal-carbonbond of the bridging isocyanide. The reaction takes place witha variety of alkynes, except for HCtC(CO2Me), which yieldsan unprecedented ferrocene-like complex. The insertion ofmonosubstituted alkynes is regiospecific, and the C-C bondformation exclusively occurs between the less hindered al-kyne carbon and the isocyanide. The N atom in the bridgingenimine ligand can be easily protonated or alkylated, providinga route for the synthesis of new functionalized vinyliminiumcomplexes, whose reactivity parallels that of strictly relatedcomplexes.

Experimental Section

General Procedures.All reactions were routinely carried outunder a nitrogen atmosphere, using standard Schlenk techniques.Solvents were distilled immediately before use under nitrogen fromappropriate drying agents. Chromatography separations were carriedout on columns of deactivated alumina (4% w/w water). Glasswarewas oven-dried before use. Infrared spectra were recorded at 298K on a Perkin-Elmer Spectrum 2000 FT-IR spectrophotometer, andelemental analyses were performed on a ThermoQuest Flash 1112Series EA instrument. ESI MS spectra were recorded on a WatersMicromass ZQ 4000 instrument with samples dissolved in CH3-CN. All NMR measurements were performed on Varian Gemini300 and Mercury Plus 400 spectrometers. The chemical shifts for1H and13C were referenced to internal TMS. The spectra were fullyassigned via DEPT experiments and1H, 13C correlation throughgs-HSQC and gs-HMBC experiments.20 Unless otherwise stated,all NMR spectra were recorded at 298 K; NMR signals due to asecond isomeric form (when it was possible to detect and/or resolvethem) are given in italics. NOE measurements were recorded usingthe DPFGSE-NOE sequence.21 All of the reagents were commercialproducts (Aldrich) of the highest purity available and were used asreceived. [Fe2(CO)4(Cp)2] was purchased from Strem and used asreceived. The compounds [Fe2(CNMe)(CO)3(Cp)2] (1)12 and (cis,Z)-[Fe2{µ-C(Et)dC(Et)CdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][CF3SO3] (3)were prepared by published methods.5b Crystals of3 suitable forX-ray analysis were obtained by a CH2Cl2 solution layered withdiethyl ether, at-20 °C.

Synthesis of (Z)-[Fe2{µ-η1:η3-C(R)C(R′)CdN(Me)}(µ-CO)-(CO)(Cp)2] (R ) R′) Ph, 2a; R ) R′ ) Me, 2b; R ) R′ ) Et,2c; R ) Ph, R′ ) H, 2d; R ) C6H4Me (Tol), R′ ) H, 2e; R )SiMe3, R′ ) H, 2f; R ) Me, R′ ) H, 2g; R ) CH2OH, R′ ) H,2h). A solution of [Fe2(CNMe)(CO)3(Cp)2] (1; 310 mg, 0.845mmol), in diethyl ether (25 mL), was treated with PhCtCPh (306mg, 1.72 mmol) and irradiated by a UV lamp for 6 h. Hence, themixture was chromatographed on alumina, and a band correspond-ing to 2a was collected with THF. The product was obtained as anemerald green powder upon removal of the solvent under reducedpressure. Yield: 245 mg, 56%. Anal. Calcd for C28H23Fe2NO2: C,65.03; H, 4.48; N, 2.71. Found: C, 65.13; H, 4.42; N, 2.70. IR(CH2Cl2): ν(CO) 1972 (vs), 1778 (s),ν(CdN) 1729 (w) cm-1. 1HNMR (CDCl3): δ 8.10-7.00 (m, 3 H, Me2C6H3 and Ph); 4.86,4.56 (s, 10 H, Cp); 3.85 (s, 3 H, NMe).13C{1H} NMR (CDCl3):δ 264.8 (µ-CO); 211.9 (CO); 192.5 (CR); 188.5 (Cγ); 155.7, 136.3(ipso-Ph); 130.6, 128.5, 127.9, 127.8, 127.7, 126.9, 125.9, 124.8(Ph); 89.5, 85.3 (Cp); 47.6 (Câ); 41.2 (NMe).

Compounds2b-h were prepared by the same proceduredescribed for2a, by reacting1 with the appropriate alkyne. Thesynthesis of2b was performed in toluene solution. Conversion ofthe cis/trans mixtures of2b,c into the respective neat cis formswere accomplished by heating in boiling toluene solutions, for 2h. Crystals suitable for X-ray analysis were obtained by a CH2Cl2solution of2c layered withn-pentane, at-20 °C.

2b (yield 60%; reaction time 4 h; green). Anal. Calcd for C18H19-Fe2NO2: C, 55.01; H, 4.87; N, 3.56. Found: C, 54.09; H, 4.87; N,3.52. IR (CH2Cl2): ν(CO) 1966(s), 1954 (vs), 1796 (s),ν(CdN)1714 (m) cm-1. 1H NMR (CDCl3): δ 4.84, 4.58,4.54, 4.37 (s, 10H, Cp); 3.81,3.77(s, 3 H, CγMe); 3.75,3.68(s, 3 H, NMe);1.59,1.46 (s, 3 H, CâMe). Trans/cis ratio 6:5.13C{1H} NMR (CDCl3):δ 266.9, 265.2 (µ-CO);211.9, 211.6 (CO);197.3, 193.8 (CR); 196.0(Cγ); 88.5, 88.3,88.0, 85.0(Cp); 49.2,48.9(Câ); 41.4, 36.2 (NMe);35.7, 35.1 (CγMe); 16.9, 15.0 (CâMe).

2c (yield 64%; reaction time 3 h; emerald green). Anal. Calcdfor C20H23Fe2NO2: C, 57.05; H, 5.51; N, 3.33. Found: C, 57.12;

(20) Wilker, W.; Leibfritz, D.; Kerssebaum, R.; Beimel, W.Magn. Reson.Chem.1993, 31, 287.

(21) Stott, K.; Stonehouse, J.; Keeler, J.; Hwang, T. L.; Shaka, A. J.J.Am. Chem. Soc.1995, 117, 4199.

Scheme 6

Diiron µ-Vinyliminium Complexes Organometallics, Vol. 26, No. 14, 20073453

H, 5.55; N, 3.28. IR (CH2Cl2): ν(CO) 1964 (s),1940 (vs), 1780(s), 1773 (m),ν(CdN) 1718 (w), 1715 (w) cm-1. 1H NMR(CDCl3): δ 4.82, 4.54,4.52, 4.38(s, 10 H, Cp);4.21, 4.11 (m, 2H, CγCH2); 3.74, 3.70 (s, 3 H, NMe); 2.45, 1.30 (m, 2 H, CâCH2);1.71(dd, 3 H,3JHH ) 7.32 Hz,3JHH ) 7.69 Hz, CγCH2CH3); 1.64(dd, 3 H,3JHH ) 7.32 Hz,3JHH ) 7.32 Hz, CγCH2CH3); 1.19 (m,3 H, CâCH2CH3); 1.10 (dd, 3 H,3JHH ) 7.32 Hz,3JHH ) 7.69 Hz,CâCH2CH3). Cis/trans ratio 5:2.13C{1H} NMR (CDCl3): δ 265.8,264.2(µ-CO); 212.6, 212.1 (CO); 201.6,198.9(Cγ); 195.4, 192.3(CR); 88.2, 87.8,86.3, 84.4 (Cp); 54.3,50.8(Câ); 42.7, 41.7 (NMe);42.6, 42.2 (CγCH2); 24.4, 23.7 (CâCH2); 18.8,18.5 (CγCH2CH3);12.5, 12.1 (CâCH2CH3).

2d (yield 55%; reaction time 3.5 h; green). Anal. Calcd forC22H19Fe2NO2: C, 59.91; H, 4.34; N, 3.18. Found: C, 59.98; H,4.26; N, 3.08. IR (CH2Cl2): ν(CO) 1970 (vs), 1778 (s),ν(CdN)1732 (w) cm-1. 1H NMR (CDCl3): δ 8.05-7.31 (m, 5 H, Ph);4.82, 4.64 (s, 10 H, Cp); 3.82 (s, 3 H, NMe); 2.99 (s, 1 H, CâH).13C{1H} NMR (CDCl3): δ 264.2 (µ-CO); 211.5 (CO); 196.7 (Cγ);192.2 (CR); 157.6 (ipso-Ph); 128.0, 127.9, 125.9 (Ph); 88.7, 84.8(Cp); 41.6 (NMe); 35.0 (Câ).

2e(yield 60%, reaction time 2.5 h; brownish green). Anal. Calcdfor C23H21Fe2NO2: C, 60.70; H, 4.65; N, 3.08. Found: C, 60.66;H, 4.68; N, 3.12. IR (CH2Cl2): ν(CO) 1969 (vs), 1778 (s),ν(CdN) 1730 (w) cm-1. 1H NMR (CDCl3): δ 7.64, 7.28 (d, 4 H,3JHH

) 8.0 Hz, C6H4Me); 4.80, 4.64 (s, 10 H, Cp); 3.81 (s, 3 H, NMe);2.96 (s, 1 H, CâH); 2.45 (s, 3 H, C6H4Me). 13C{1H} NMR(CDCl3): δ 264.5 (µ-CO); 211.6 (CO); 197.0 (Cγ); 192.6 (CR);154.9 (ipso-C6H4Me); 135.5, 129.2, 128.6, 127.9 (C6H4Me); 88.8,84.8 (Cp); 41.6 (NMe); 35.0 (Câ); 21.1 (C6H4Me).

2f (yield 60%; reaction time 5 h; brownish green). Anal. Calcdfor C19H23Fe2NO2Si: C, 52.20; H, 5.30; N, 3.20. Found: C, 52.23;H, 5.25; N, 3.26. IR (CH2Cl2): ν(CO) 1974 (vs), 1789 (s) cm-1.1H NMR (CDCl3): δ 5.02, 4.70 (s, 10 H, Cp); 3.76 (s, 3 H, NMe);3.19 (s, 1 H, CâH); 0.59 (s, 9 H, SiMe3). 13C{1H} NMR (CDCl3):δ 261.1 (µ-CO); 210.6 (CO); 191.8 (CR); 179.7 (Cγ); 87.4, 86.1(Cp); 41.4 (NMe); 38.3 (Câ); 2.9 (SiMe3).

2g (yield 61%; reaction time 9 h; green). Anal. Calcd for C17H17-Fe2NO2: C, 53.87; H, 4.52; N, 3.70. Found: C, 53.80; H, 4.49; N,3.74. IR (CH2Cl2): ν(CO) 1972 (vs), 1780 (s),ν(CdN) 1727 (w)cm-1. 1H NMR (CDCl3): δ 4.88, 4.60 (s, 10 H, Cp); 3.85 (s, 3 H,NMe); 3.73 (s, 3 H, CγMe); 2.88 (s, 1 H, CâH). 13C{1H} NMR(CDCl3): δ 263.2 (µ-CO); 211.9 (CO); 195.8 (Cγ); 192.0 (CR);88.0, 86.6 (Cp); 41.0 (NMe); 37.6 (Câ); 38.9 (CγMe).

2h (yield 59%; reaction time 7 h; green). Anal. Calcd for C17H17-Fe2NO3: C, 51.69; H, 4.34; N, 3.55. Found: C, 51.62; H, 4.39; N,3.58. IR (CH2Cl2): ν(CO) 1978 (vs), 1789 (s),ν(CdN) 1740 (w)cm-1. 1H NMR (CD3CN): δ 6.15, 5.88 (d, 2 H,2JHH ) 14.6 Hz,CH2OH); 5.14, 4.75 (s, 10 H, Cp); 5.06 (br, 1 H, OH); 3.48 (s, 3H, NMe); 2.85 (s, 1 H, CâH). 13C{1H} NMR (CD3CN): δ 264.2(µ-CO); 212.1 (CO); 196.7 (Cγ); 191.9 (CR); 89.3, 88.5 (Cp); 74.9(CH2OH); 45.6 (NMe); 35.3 (Câ).

Synthesis of [Fe2{µ-η2:η4-C(OH)C(CO2Me)C(H)CN(Me)-(CHdCHCO2Me}(CO)(Cp)2] (4). This product was prepared bythe same procedure described for2a-h, by reacting1 (185 mg,0.365 mmol) with HCtCCO2Me (3.6 mmol): reaction time 6 h;green; yield 104 mg (56%). Anal. Calcd for C22H23Fe2NO6: C,51.90; H, 4.55; N, 2.75. Found: C, 51.92; H, 4.47; N, 2.60. IR(CH2Cl2): ν(CO) 1965 (vs), 1686 (m), 1672 (m),ν(CdC) 1601(vs) cm-1. 1H NMR (CDCl3): δ 10.00 (s, 1 H, OH); 8.35 (d, 2 H,3JHH ) 13.54 Hz,HCdCHCO2Me); 4.90 (d, 2 H,3JHH ) 13.54Hz, HCdCHCO2Me); 5.24 (s, 1 H, CâH); 4.94, 4.31 (s, 10 H, Cp);3.74 (s, 6 H, COOMe); 3.31 (s, 3 H, NMe).13C{1H} NMR(CDCl3): δ 218.8 (CO); 216.6 (COH); 179.0 (CR); 176.2, 169.6(COOMe); 152.5 (HCdCHCO2Me); 87.9 (HCdCHCO2Me); 84.1,77.7 (Cp); 79.3 (Câ); 67.2 (Cγ); 51.7, 50.8 (COOMe); 40.0 (NMe).

Synthesis of [Fe2{µ-η1:η3-C(R)dC(R)CdN(Me)(H)}(µ-CO)-(CO)(Cp)2][BF4] (R ) Ph, 5a; R ) Et, 5b). A solution of 2a

(100 mg, 0.193 mmol) in CH2Cl2 (10 mL) was treated with HBF4(0.20 mmol). The mixture was stirred for 10 min, and then thesolvent was removed under reduced pressure. The residue waswashed with diethyl ether (2× 10 mL) and dissolved in CH2Cl2,and this solution was filtered on a Celite pad. The product wasobtained as dark brown crystals upon removal of the solvent.Yield: 106 mg (91%). Crystals suitable for X-ray analysis wereobtained by a CH3CN solution of5a layered with diethyl ether, at-20 °C. Anal. Calcd for C28H24BF4Fe2NO2: C, 55.59; H, 4.00; N,2.32. Found: C, 55.56; H, 4.08; N, 2.26. IR (KBr pellets):ν(NH)3246 (m) cm-1. IR (CH2Cl2): ν(CO) 2004 (vs), 1804 (s),ν(CdN)1674 (m) cm-1. 1H NMR (CDCl3): δ 10.37 (br, 1 H, NH); 7.82-6.81 (m, 10 H, Ph); 5.32,5.24, 4.98,4.91(s, 10 H, Cp);3.77, 2.59(d, 3JHH ) 4.94 ppm, 3 H, NMe).E/Z ratio 8:5. 13C{1H} NMR(CDCl3): δ 255.4, 252.6 (µ-CO); 226.5 (CR); 210.2,208.4(CO);200.8,198.9(Cγ); 153.5, 153.2 (ipso-Ph); 132.8-123.7 (Ph);91.9,91.7, 88.6,87.5 (Cp); 71.8 (Câ); 39.7,37.1 (NMe).

Compound5b was prepared by the same procedure describedfor 6a, by reacting2c (88 mg, 0.209 mmol) with HBF4 (0.25 mmol):yield: 98 mg (92%); green. Anal. Calcd for C20H24BF4Fe2NO2:C, 47.20; H, 4.75; N, 2.75. Found: C, 47.16; H, 4.79; N, 2.83. IR(KBr pellets): ν(NH) 3226 (m) cm-1. IR (CH2Cl2): ν(CO) 2000(s), 1978 (vs),1807 (m), 1789 (s),ν(CdN) 1671 (m) cm-1. 1HNMR (CDCl3): δ 10.09 (s br, 1 H, NH);5.15, 4.84, 4.75, 4.61 (s,10 H, Cp);4.34, 4.06, 4.12, 4.02 (m, 2 H, CγCH2); 3.78,3.24 (s,3 H, NMe); 2.72,2.51, 2.01, 1.88 (m, 2 H, CâCH2); 1.86, 1.68 (m,3 H, CγCH2CH3); 1.20, 1.18 (m, 3 H, CâCH2CH3). Trans/cis ratio6:1. 13C{1H} NMR (CDCl3): δ 254.5 (µ-CO); 223.8 (CR); 209.2(CO); 203.0 (Cγ); 89.4, 88.0 (Cp); 74.3 (Câ); 43.5 (NMe); 37.7(Cγ-CH2); 23.5 (Câ-CH2); 18.2 (CγCH2CH3); 12.8 (CâCH2CH3).

Synthesis of [Fe2{µ-η1:η3-C(Ph)dC(Ph)CdN(Me)(CH2CHdCH2)}(µ-CO)(CO)(Cp)2][I] (6). CH2CHCH2I (0.70 mmol) wasadded to a solution of2a (90 mg, 0.174 mmol) in CH2Cl2 (10 mL).The mixture was stirred for 20 min, and then the solvent wasremoved. Chromatography of the residue on alumina, with MeOHas eluent, afforded a red band corresponding to7. Yield: 99 mg(83%). Anal. Calcd for C31H28Fe2INO2: C, 54.34; H, 4.12; N, 2.04.Found: C, 54.32; H, 4.12; N, 2.07. IR (CH2Cl2): ν(CO) 1994 (vs),1813 (s),ν(CdN) 1653 (m),ν(CdC) 1637 (w) cm-1. 1H NMR(CDCl3): δ 7.64-7.03 (m, 10 H, Ph); 5.94,5.27 (m, 1 H,NCH2CH); 5.51,5.46, 5.11, 5.10 (s, 10 H, Cp); 5.50,5.28 (m, 2H, NCH2CHCH2); 4.97 (m, 1 H, NCH2CH); 4.02, 2.63 (s, 3 H,NMe); 3.66, 3.63, 3.48,3.44 (m, 2 H, NCH2). E/Z ratio 6:5.13C-{1H} NMR (CDCl3): δ 254.8, 254.1 (µ-CO); 224.7,223.9 (CR);210.2,209.9(CO); 201.1,201.0(Cγ); 152.9 (ipso-Ph); 133.0-122.8(Ph); 123.0,122.8 (NCH2CHCH2); 122.9 (NCH2CHCH2); 92.1,92.0, 88.4,88.3 (Cp); 72.4, 72.1 (Câ); 64.8, 61.6 (NCH2); 44.6,42.8 (NMe). ESI-MS (ES+): m/z 558. ESI-MS (ES-): m/z 127.

Synthesis of [Fe2{µ-η1:η3-C(Ph)dC(Ph)CdN(Me)(CO2Me)}-(µ-CO)(CO)(Cp)2][Cl] (7). ClC(O)OMe (0.90 mmol) was addedto a solution of2a (95 mg, 0.184 mmol) in CH2Cl2 (15 mL), andthe mixture was stirred for 20 min. Removal of the volatile materialsgave7 as a red microcrystalline powder. Yield: 90 mg (80%). Anal.Calcd for C30H26ClFe2NO4: C, 58.91; H, 4.28; N, 2.29. Found:C, 58.97; H, 4.24; N, 2.25. IR (CH2Cl2): ν(CO) 2007 (vs), 1832(s), 1774 (s),ν(CdN) 1556 (m) cm-1. 1H NMR (CDCl3): δ 8.10-6.75 (m, 10 H, Ph); 5.19, 5.10 (s, 10 H, Cp); 4.18 (s, 3 H, CO2-Me); 3.28 (s, 3 H, NMe).13C{1H} NMR (CDCl3): δ 249.2 (µ-CO); 217.0 (CR); 207.9 (CO); 202.5 (Cγ); 161.3 (CO2Me); 152.9(ipso-Ph); 146.6-124.6 (Ph); 94.2, 91.7 (Cp); 71.9 (Câ); 55.4(CO2Me); 43.0 (NMe).

Synthesis of [Fe2{µ-η1:η3-C(Ph)C(Ph)dC(H)N(Me)(CH2CHdCH2)}(µ-CO)(CO)(Cp)2] (8). Complex6 (50 mg, 0.0730 mmol)was dissolved in THF (10 mL) and treated with NaBH4 (14 mg,0.368 mmol). The mixture was stirred for 15 min, and then it wasfiltered on alumina. Solvent removal and chromatography of theresidue on alumina, with CH2Cl2 as eluent, gave a green band

3454 Organometallics, Vol. 26, No. 14, 2007 Albano et al.

corresponding to8. Yield: 35 mg (86%). Anal. Calcd for C31H29-Fe2NO2: C, 66.58; H, 5.23; N, 2.50. Found: C, 66.52; H, 5.29; N,2.58. IR (CH2Cl2): ν(CO) 1933 (vs), 1754 (s),ν(CdC) 1591 (w)cm-1. 1H NMR (CDCl3): δ 8.19-6.65 (m, 10 H, Ph); 5.91 (m, 1H, NCH2CH); 5.15 (m, 2 H, NCH2CHCH2); 4.85, 4.32 (s, 10 H,Cp); 3.21 (m, 2 H, NCH2); 1.90 (s, 3 H, NMe); 0.91 (s, 1H, CRH).13C{1H} NMR (CDCl3): δ 278.7 (µ-CO); 217.8 (CO); 185.8 (Cγ);156.7 (ipso-C6H4Me); 139.7, 134.5, 131.3, 129.2, 128.8, 127.1,125.6, 123.2 (Ph); 123.3 (NCH2CH); 117.9 (NCH2CHCH2); 97.3(CR); 88.6, 81.8 (Cp); 83.7 (Câ); 59.6 (NCH2); 38.6 (NMe).

Synthesis of [Fe2{µ-η1:η3-C(Ph)C(Ph)C(CN)N(Me)(CH2CHdCH2)}(µ-CO)(CO)(Cp)2] (9). NBut

4CN (23 mg, 0.0858 mmol) wasadded to a solution of6 (48 mg, 0.0701 mmol) in CH2Cl2 (15 mL).The mixture was stirred for 30 min, and then it was filtered onalumina. The product was obtained as a red powder upon removalof the solvent under reduced pressure. Yield: 36 mg (88%). Anal.Calcd for C32H28Fe2N2O2: C, 65.78; H, 4.83; N, 4.79. Found: C,65.66; H, 4.79; N, 4.88. IR (CH2Cl2): ν(CtN) 2187 (w),ν(CO)1972 (vs), 1788 (s),ν(CdC) 1591 (w) cm-1. 1H NMR (CDCl3): δ7.95-7.02 (m, 10 H, Ph); 5.73,5.72 (m, 1 H, NCH2CH); 5.12,5.04 (m, 2 H, NCH2CHCH2); 4.82, 4.80, 4.57 (s, 10 H, Cp); 4.13,3.10, 2.99, 2.80 (dd, 2 H,2JHH ) 12.8 Hz,3JHH ) 2.9 Hz, NCH2);2.48, 2.05 (s, 3H, NMe). Isomer ratio 6:5.13C{1H} NMR(CDCl3): δ 264.6, 264.1 (µ-CO); 213.4, 213.0 (CO);197.6, 197.1(Cγ); 157.3,157.2 (ipso-Ph);139.6, 139.4, 135.6,134.8, 132.1,128.2,128.0, 127.9, 127.8, 127.2, 126.9, 126.6 (Ph);124.1, 124.0(NCH2CH); 120.2, 120.0 (CtN); 118.0, 117.2 (NCH2CHCH2);90.6, 90.4, 87.2, 87.1 (Cp); 96.6,95.7 (Câ); 65.8, 59.3 (NCH2);64.2, 63.0 (CR); 45.9,39.9 (NMe).

X-ray Crystallography. The X-ray intensity data for2c, 3, 4‚CH2Cl2, and5a were measured on a Bruker AXS SMART 2000diffractometer, equipped with a CCD detector. Cell dimensions andthe orientation matrix were initially determined from a least-squaresrefinement on reflections measured in 3 sets of 20 exposures,collected in 3 differentω regions, and eventually refined againstall data. For all crystals, a full sphere of reciprocal space wasscanned by 0.3° ω steps, with the detector kept at 5.0 cm from thesample. The software SMART22 was used for collecting frames ofdata, indexing reflections, and determining lattice parameters. Thecollected frames were then processed for integration by the SAINTprogram,22 and an empirical absorption correction was applied using

SADABS.23 The structures were solved by direct methods (SIR97)24 and subsequent Fourier syntheses and refined by full-matrixleast squares onF2 (SHELXTL),25 using anisotropic thermalparameters for all non-hydrogen atoms except the cyclopentadienylligands in4. In 3, some disorder was detected for both the fluorineand oxygen atoms of the CF3SO3

- group, which were refined overtwo sites, yielding occupation factors of 0.55 and 0.57 for the mainimages of the F atoms bound to C(39) and O atoms bound to S,respectively. Crystals of4 were found to contain one CH2Cl2molecule in the asymmetric unit. In the solid state5a is present intwo conformers. In both conformers one cyclopentadienyl ring(bound to Fe(2)) is disordered over two positions and the siteoccupation factors were refined to 0.69 for the main image in bothconformers. All hydrogen atoms, except the hydrogen bound toO(1) in 4 and to N(1) in5a, which were found in the Fourier mapand refined isotropically, were added in calculated positions,included in the final stage of refinement with isotropic thermalparameters,U(H) ) 1.2 Ueq(C) (U(H) ) 1.5 Ueq(C-Me)), andallowed to ride on their carrier carbons. Crystal data and details ofthe data collection for all structures are reported in Table 3.

Acknowledgment. We thank the Ministero dell’Universita`e della Ricerca (MUR; project “New strategies for the controlof reactions: interactions of molecular fragments with metallicsites in unconventional species”) and the University of Bolognafor financial support.

Supporting Information Available: CIF files giving X-raycrystallographic data for the structure determinations of2c, 3, 4‚CH2Cl2, and5a. This material is available free of charge via theInternet at http://pubs.acs.org.

OM070097Z

(22)SMART & SAINT Software Reference Manuals,Version 5.051(Windows NT Version); Bruker Analytical X-ray Instruments Inc.: Madison,WI, 1998.

(23) Sheldrick, G. M. SADABS, Program for Empirical AbsorptionCorrection; University of Go¨ttingen, Gottingen, Germany, 1996.

(24) Altomare, A.; Burla, M. C.; Cavalli, M.; Cascarano, G. L.;Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,R. J. Appl. Crystallogr.1999, 32, 115.

(25) Sheldrick, G. M. SHELXTLplusVersion 5.1 (Windows NT version)Structure Determination Package; Bruker Analytical X-ray Instruments Inc.,Madison, WI, 1998.

Table 3. Crystal Data and Experimental Details for 2c, 3, 4‚CH2Cl2, and 5a

2c 3 4‚CH2Cl2 5a

formula C20H23Fe2NO2 C29H32F3Fe2NO5S C23H25Cl2Fe2NO6 C28H24BF4Fe2NO2

fw 421.09 675.32 594.04 604.99T, K 296(2) 296(2) 296(2) 296(2)λ, Å 0.71073 0.71073 0.71073 0.71073cryst syst monoclinic triclinic monoclinic monoclinicspace group P21/c P1h P21/c P21/na, Å 9.693(2) 8.2804(3) 9.0847(18) 13.911(3)b, Å 12.446(3) 12.4402(4) 35.133(7) 22.709(5)c, Å 15.295(3) 15.0634(5) 8.4489(17) 17.018(3)R, deg 90 107.4700(10) 90 90â, deg 91.781(5) 101.8190(10) 115.43(3) 101.16(3)γ, deg 90 91.7950(10) 90 90cell vol, Å3 1844.3(7) 1441.55(8) 2435.4(8) 5274.5(18)Z 4 2 4 8Dc, g cm-3 1.517 1.556 1.620 1.524µ, mm-1 1.585 1.138 1.450 1.155F(000) 872 696 1216 2464cryst size, mm 0.25× 0.23× 0.21 0.28× 0.25× 0.23 0.25× 0.21× 0.15 0.23× 0.19× 0.14θ limits, deg 2.66-28.70 2.53-28.00 2.55-25.00 1.51-25.03no. of rflns collected 21 343 (Rint ) 0.0610) 16 496 (Rint ) 0.0291) 18 651 (Rint ) 0.1111) 46 377 (Rint ) 0.0740)no. of indep rflns 4754 6926 3765 9319goodness of fit onF2 1.102 1.042 1.131 1.048R1 (I > 2σ(I))a 0.0604 0.0660 0.0817 0.0592wR2 (all data)b 0.1625 0.2112 0.1850 0.1787largest diff peak and hole, e Å-3 1.103/-1.800 1.264/-0.919 0.997/-0.769 0.880/-0.700

a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo2 - Fc

2)2/∑w(Fo2)2]1/2, wherew ) 1/[σ2(Fo

2) + (aP)2 + bP], whereP ) (Fo2 + 2Fc

2)/3.

Diiron µ-Vinyliminium Complexes Organometallics, Vol. 26, No. 14, 20073455